1. Field of the Disclosure
This disclosure relates generally to a timing recovery circuit in a receiver for recovering clock timing from a received signal and, more particularly, to a digital timing recovery circuit in a receiver where the circuit is able to recover clock timing for both continuous phase modulated and linear stream modulated signals by providing signal down-conversion and filtering prior to a squaring non-linearity process.
2. Discussion of the Related Art
Digital signals can be wirelessly transmitted from a transmitter to a receiver where data and other information can be recovered. However, there is typically a discrepancy between the sample clock in the transmitter that transmitted the signal and the sample clock in the receiver that receives the signal that causes inter-symbol interference (ISI), and possible loss of data. Therefore, symbol timing recovery must be performed in front-end circuitry of the receiver to sufficiently recover the data in the received signal. For non-data-aided timing recovery, the timing information is encoded on a carrier frequency using symbols that are defined by changes in amplitude and phase of the transmitted signal. Timing recovery requires that the circuit identify when those changes in phases and amplitude occur in the signal.
The digital data is encoded on the carrier wave by different modulation schemes, including continuous phase modulation and linear stream modulation, well known to those skilled in the art. Traditional communications system use different timing recovery synchronization architectures for continuous phase modulation and linear stream modulation transmission protocols. The traditional timing recovery architecture that provided linear stream modulation typically included passing the received signal through a non-linearity circuit to generate a signal oscillating at the clock frequency. This signal is filtered and in-phase and quadrature phase (I/Q) down-converted to produce a time estimate.
One known down-converting methodology is referred to in the art as Fs/4 down-conversion that down-converts a received signal to an intermediate frequency (IF) to produce both the in-phase and quadrature phase components of the signal. However, known timing recovery circuits in receiver front-ends are typically unable to provide Fs/4 down-conversion for both continuous phase modulation and linear stream modulation.